This application is based on Japanese Patent Application No. 10-304953 (1998) filed Oct. 27, 1998, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink-jet printing apparatus, an ejection recovery method for the ink-jet printing apparatus, and a fabrication method of an ink-jet printing head.
The present invention intends for an ink-jet printing head, ink-jet printing head cartridge, and ink-jet printing apparatus to be used for a printer or video printer serving as an output terminal of a copying machine, a facsimile, a word processor, or a host computer. Particularly, the present invention intends for an ink-jet printing head having a substrate on which an electrothermal device for generating thermal energy used as the energy for ejecting ink is formed and a printing apparatus using the printing head. In this case, the concept of printing includes supply of ink (printing) to all ink supports to which ink is supplied such as cloth, yarn, paper, and sheet and moreover, includes not only a meaningful picture such as a character but also a pattern picture. A printing apparatus includes every type of information processor or a printer serving as an output unit of the information processor and the present invention can be applied to these purposes.
2. Description of the Related Art
A liquid-jet printing method performs printing by forming flying droplets of a printing liquid such as ink and attaching the droplets to a printing media to be printed such as paper or the like. A liquid-jet printing apparatus using the above printing method realizes low-noise high-speed printing and high-density printing. Moreover, the printing apparatus can be downsized because developing or fixing process is unnecessary for plain paper. Furthermore, this type of liquid-jet printing apparatus is particularly noticed because the productivity of the printing apparatus is high under mass production and the printing apparatus manufacturing cost is low.
To form the above flying droplets, a liquid-jet printing head using thermal energy is provided with an electrothermal transducer as means for heating a printing liquid. That is, the printing head has an exothermic resistor (hereafter referred to as xe2x80x9cheaterxe2x80x9d) capable of heating the printing liquid by producing heat when an electric signal is applied and a pair of electrodes for applying an electric signal to the exothermic resistor. The printing liquid is bubbled due to the heat generated by the heater and is ejected from an ink ejection port by the bubbling energy. Moreover, the printing liquid used in the above case is generally configured by a printing component such as a pigment or dye and water for dissolving or dispersing the printing component or a solvent component comprising water and a water-soluble organic solvent.
In case of the above water-based printing liquid, a heating limit for sudden evaporation ranges between 250 and 350xc2x0 C. The heating limit temperature is equal to a temperature at which vapor is produced due to the calorie conducted to the printing liquid through a very thin and stable vapor film between the surface of the heater and the printing liquid. Therefore, to form flying droplets and record them to a printing media to be printed by using the printing liquid having the above temperature characteristic, and supplying an electric signal to the heater and bubbling the printing liquid and thereby evaporating the printing liquid, the heater is repeatedly heated at a temperature in the range from ambient temperature up to 300 to 800xc2x0 C. each time when an electric signal is supplied.
A heater and an electrode or the like are formed in accordance with a semiconductor process. For example, a wiring portion made of a metal serving as an electrical good conductor (e.g. electrode made of Al, Au, Ag, or Cu) is formed on an exothermic resistor (e.g. heat-resistant resistor made of HfB2, ZrB2, TaN2, or TaSi) set on a substrate (e.g. made of Si, glass, or ceramic) through an intermediate layer (e.g. made of Ti or Cr). The wiring portion is formed by laminating the intermediate layer so as to be exposed in part and the exposed portion servers as a heater. Moreover, a protective film superior in heat resistance and printing-liquid cutoff characteristic for preventing electrolytic corrosion or oxidation due to the printing liquid is formed on the heater and electrode at need.
The above printing head ejects a printing liquid by applying an electric signal corresponding to a printing signal to a heater and repeatedly making the heater produce heat at a high temperature to heat the printing liquid. For a printing head having the above configuration and a printing apparatus provided with the printing head, treatments for improving the printing characteristics under printing (particularly, characteristics of a printing liquid such as viscosity, surface tension, and density or the like) are proposed.
The above treatments have been performed so far by a printing mode including the preliminary ejecting shown in U.S. Pat. No. 4,712,172 or a printing mode including the preliminary heating shown in U.S. Pat. Nos. 4,463,359, 4,296,421, 4,719,472, and 4,712,172 while a liquid-jet printing head is set to a printing apparatus. Each of these treatments ejects ink not contributing to printing of pictures from a printing head to recover an ink ejecting condition. Hereafter, the above ejection recovery is also referred to as xe2x80x9cpreliminary ejecting.xe2x80x9d
By performing the above treatments, the ejecting characteristic of a printing liquid under the printing operation is improved. However, these treatments are not sufficient to obtain the best printing state at the initial stage of using a printing head. Because a heater is repeatedly made to produce heat at a high temperature in the printing mode including the above preliminary ejecting and preliminary heating, phase change, stress change, oxidation, and composition change of the heater material are caused and moreover, resistance-value change occurs in the heater material. Furthermore, resistance distribution change of the heater material occurs due to the interface resistance between the heater material and a wiring portion (electrode) and the diffusion between both. Therefore, to improve the problems, a fabrication method of a liquid-jet printing head is disclosed in Japanese Patent Application Laying-Open No. 2-78554 (1990). This is a method of heating a heater material by applying to the heater an electric signal enough to stabilize the resistance value of the heater material in the aging process and thereby ink is ejected.
Thus, a preferable and stable ink ejecting condition can always be obtained even in long-time printing by the preliminary ejecting process for ejecting ink not contributing to printing of pictures from the ink-jet printing head mounted on an ink-jet printing apparatus, and by heating a heater material in the aging process when the ink-jet printing head is fabricated.
Because the frequency for handling image pictures has been recently increased, a request for high-picture-quality color printing, particularly for half-tone picture printing has been raised.
To express a halftone by an ink-jet printing apparatus, there is a method of expressing the halftone in accordance with the number of ink droplets applied to predetermined pixels on a printing medium (false halftone expression in accordance with binary numbers). Moreover, there is another method of expressing a halftone by using a plurality of printing heads with ejecting quantities different from each other or a plurality of printing heads capable of ejecting inks with densities different from each other and thereby, selecting and driving a printing head in accordance with the halftone. In case of these methods, however, it may be impossible to greatly raise the reliquid or a printing apparatus may be increased in size because a plurality of printing heads are used. Therefore, an ink-jet printing apparatus is requested which requires less space and realizes high-reliquid printing at a low cost by changing eject quantities of one printing head at various levels.
To attain the above object, Japanese Patent Application Publication No. 62-48585 (1987) discloses a gradation printing method of realizing high-picture-quality printing by changing sizes of ejected ink droplets. In case of this printing method, a plurality of heaters with areas different from each other are arranged in an ink passage to independently control each heater.
However, to realize the so-called multiple-heater ink-jet printing head in which a plurality of heaters are arranged in an ink passage, there are some problems.
First, there are requests for improving the ink ejecting reliability and the ink-droplet impact accuracy immediately after ink eject when the time of ejecting no ink is long by improving the ink ejecting speed in order to not only make the ink ejecting quantity changeable but also perform higher-quality printing. Particularly, when a multiple-heater ink-jet printing head is used, there are some cases in which it is difficult to increase the ink ejecting speed of relatively small droplets in volume in order to eject the droplets from a relatively large ink ejection port. In this case, ink ejection may be disturbed due to accidental imperfect bubbling or the state nearby the ink ejection port. A small-droplet-ejecting heater having a small heater area easily influences ink ejection even due to a small foreign matter on the heater surface. Therefore, there are some cases in which the existing preliminary ejecting process or heating in the aging process is insufficient to stably eject small droplets. Moreover, the preliminary ejecting process or heating in the aging process has an advantage of removing a foreign matter or the like from the surface of a heater. In the case of a multiple-heater ink-jet printing head, however, when above preliminary ejecting process or heating in the aging process is performed by simultaneously driving a plurality of heaters, the position where a bubble for ejecting ink disappear is frequently deviated from the center of a heater. Therefore, the cavitation effect for removing burnt deposits or foreign matters from the surface of a heater frequently lowers.
It is an object of the present invention to more stably maintain the ejecting characteristics including the ejecting speed and ejecting quantity of ink under the picture printing operation of driving a plurality of electrothermal transducers and thereby ejecting ink by effectively applying ejection recovery and aging to an ink-jet printing head provided with the electrothermal transducers for one ink passage.
In the first aspect of the present invention, there is provided an ink-jet printing apparatus for printing an image on a printing medium by using an ink-jet printing head capable of ejecting ink from an ink ejection port communicating with an ink passage, and capable of generating a bubble in ink of the ink passage by the heat produced by a plurality of electrothermal transducers set to the ink passage, wherein
control means is included which changes shift values of the heat-producing timings of the electrothermal transducers by changing shift values of driving signals to be applied to the electrothermal transducers when ejecting the ink not contributing to printing of the image from the ink-jet printing head to recover an ink ejecting condition.
In the second aspect of the present invention, there is provided an ejection recovery method for an ink-jet printing apparatus for printing an image on a printing medium by using an ink-jet printing head capable of ejecting ink from an ink ejection port communicating with an ink passage, and capable of generating a bubble in ink of the ink passage by the heat produced by a plurality of electrothermal transducers set to the ink passage, comprising the step of:
changing shift values of driving signals to be applied to a plurality of electrothermal transducers and thereby changing shift values of heat-producing timings of the electrothermal transducers when performing ejection recovery for recovering an ink ejecting condition by ejecting the ink not contributing to printing of the image from the ink-jet printing head.
In the third aspect of the present invention, there is provided a fabrication method of an ink-jet printing head capable of ejecting ink from an ink ejection port communicating with an ink passage by generating a bubble in the ink of an ink passage by the heat produced by a plurality of electrothermal transducers set to the ink passage, comprising the step of:
changing shift values of driving signals to be applied to the electrothermal transducers and thereby changing shift values of heat-producing timings of the electrothermal transducers when ejecting ink from the ink-jet printing head for aging process.
In case of the present invention, an ink-jet printing head provided with a plurality of electrothermal transducers for one ink passage shifts the application timing of a driving signal to be applied to each of the electrothermal transducers in the ejection recovery of an ink-jet printing head while the head is set to an ink-jet printing apparatus or the aging of the head while being fabricated. Thereby, it is possible to decrease long-term deterioration of the printing quality and to improve the printing quality at the initial stage after fabrication.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.